86 Diseases of Truck Crops 



Mode of Infection and Period of Incubation. Mosaic 

 may be readily transmitted from plant to plant. 

 The easiest way to prove this is to rub with the rin- 

 gers a diseased plant, and then immediately rub a 

 healthy plant. The disease will appear on the in- 

 oculated host in about ten days. In the field, insects 

 act as carriers of mosaic. The trucker may prevent 

 much of this trouble by proper spraying against suck- 

 ing and biting insects. 



D. DISEASES DUE TO PARASITIC BACTERIA OR 



FUNGI 



We have already seen that certain classes of 

 beneficial bacteria perform an important function 

 in the soil. This, too, must be true for certain 

 soil fungi. Not all microorganisms, however, are 

 beneficial. But, fortunately for the trucker, only a 

 small per cent, of bacteria and fungi are parasitic, 

 and produce disease on plants. On page 4 a 

 description was given of the nature and structure of 

 bacteria. Before proceeding further it becomes 

 necessary to familiarize ourselves with the nature 

 of fungi. 



Fungi. As already stated, these are low forms of 

 plant life, some of which are beneficial, while others 

 live as parasites on the higher green plants, the results 

 of which may be considered as follows : 



I. Actual death may result from the destruction 

 of vital organs or tissues. 2. A crippling and dwarf- 

 ing of plants due to the slow destruction of the root 



